When the Jurassic period began, about 199 million years ago, a lot of animals had just become extinct in the catastrophe that ended the Triassic period. This left room for the dinosaurs to have a lot of baby dinosaurs and soon the land on Earth was just covered in all different kinds of dinosaurs. The Jurassic is the main period of the dinosaurs - that's why they called the movie "Jurassic Park".
At the same time, near the beginning of the Jurassic period, the supercontinent Pangaea broke up into smaller continents that began to drift away from each other, with some tectonic plates beginning to crash into each other and form, for example, the Andes mountains in South America. So some of the dinosaurs and early mammals were isolated from the others, and different kinds of animals began to evolve on each smaller continent. But as Pangaea broke up, the dry heat of the Triassic became a more rain forest kind of climate. The climate stayed warm, as in the Triassic period, and there don't seem to have been any ice ages, or any ice at the North or South Poles. In warmer areas, the plants were mostly ferns, and in colder areas there were a lot of pine trees and ginkgo trees.
Later in the Jurassic, about 150 million years ago, the first birds evolved from small flying dinosaurs (but not from pterodactyls). Like the pterodactyls, the birds were warm-blooded.
There was no catastrophe this time, but the Jurassic period gradually changed into the Cretaceous period about 145 million years ago.
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